How to change one property (default value) on multiple materials
This script will set all &quot;Emission Strength&quot;s to 0. Copy it into the Text Editor and hit the &quot;Run&quot; button. It will affect all materials in the file, so be careful.
import bpy
for mat in bpy.data.materials:
    if not mat.use_nodes:
        continue
    for n in mat.node_tree.nodes:
        if n.type == 'BSDF_PRINCIPLED':
            n.inputs[&quot;Emission Strength&quot;].default_value = 0

Normally you do &quot;no emission&quot; with Emission Strength=1 and a black emission color though...